Low voltage ignition system for high temperature combustion chambers



06L 1960 w. B. SMITS LOW VOLTAGE IGNITION SYSTEM FOR HIGH TEMPERATURE COMBUSTION CHAMBERS Filed March 17, 1958 III ATTORNEYS United Satates Patent LOW VOLTAGE IGNITION SYSTEM FOR HIGH TEMPERATURE COMBUSTION CHAMBERS Wytze Beije Smits, Voorburg, Netherlands, assignor to Smitsnonk N.V., Leidschendam, Netherlands Filed Mar. 17, 1958, Ser. No. 721,926

4 Claims. (Cl. 313141) The invention relates to a low-voltage ignition system for the combustion chambers of jet engines, gas turbines, oil-fired plant, etc.

In this ignition system the sparking element is fitted on a bush or rod, which is secured to the wall of the combustion chamber in such a way that the sparking element is located at a distance from this wall such that it is in the right position relative to the fuel jet, to ensure good and fool-proof ignition.

The types of plant referred to above involve very high temperatures, namely, of such values that insulating materials heated to such high temperatures (even porcelain) become more or less electrically conductive. Thus it has been found that in the bush or rod, which carries the sparking element and through which was hitherto passed the electrical conductor which conducts to the tension electrode of the sparking element, leakage fluxes are apt to appear between this conductor and the earthed bush or rod, even if this conductor is very carefully insulated.

Attempts have already been made to reduce or stop these leakage fluxes, which impair or even prevent the sparking action of the element, by using a bush or rod of a large diameter, but such bushes or thick rods have the disadvantage of causing in the combustion chambers undesirable vortices in the fuel and air movement.

The invention has for its object to eliminate these drawbacks, and this is achieved by the sparking element being fitted on a thin rod or tube, which is secured to the wall of the combustion chamber. Such a thin rod or tube has the advantage of not causing the vortices in question, and this rod can be chosen as thin as possible because according to the invention the thin rod is connected in an electrically conductive manner to the inner electrode of the sparking element, while the outer electrode is connected in an electrically conductive manner to a conductor, which is connected in an insulated manner to the source of voltage through an opening in the chamber wall.

The sparking element according to the invention, used for the above-mentioned applications, consists of an annular inner electrode and a bush shaped outer electrode, one edge of which is bent inwards and faces the inner electrode, so that the sparks are able to jump between the poles over the separator body underneath. Located below the electrodes are a large number of insulating layers, e.g. of mica, and these layers are forced firmly against the inside of the bent portion of the outer electrode by a ring pressed into the bush-shaped outer electrode. The ring in question is held by the lower edge of the outer electrode being folded around it. Because the outer electrode has the shape of a bush, the height of which exceeds that of the piled-up insulating layers, the latter are protected against spattering fuel particles, while yet a favourable heat removal from the sparking element is possible. The insulating layers are also compressed between a collar of a bush and the inner electrode. In this sparking plug there are large insulating paths for surface discharge between the outer and the inner electrode, so that the whole of the ignition energy will pass over the surface of the separator body and practically no leakage fluxes, if any, will appear in the interior of the sparking element, not even at high temperatures occuring in the plant in question.

With reference to the drawing the invention is elucidated more fully for an embodiment.

Fig. 1 is a diagrammatic illustration of the system according to the invention.

Fig. 2 is a cross-section through the sparking element according to the invention.

In Fig. 1 the numeral 1 designates the sparking element, which is fitted on a thin rod 2, which is secured to the wall 3 of the combustion chamber with the aid of a nut 4. Fitted to the outer electrode of the sparking element 1 is a voltage-supply conductor 5, which passes out of the combustion chamber through a bushing insulator 6 placed between.

Fig. 2 illustrates a cross-section of the sparking element 1, and this consists of a bush-shaped outer electrode 12 and an inner electrode 11 facing the bent-back upper end thereof, said inner electrode being pressed into a bush 9, folded back at the upper and the lower end, on the separator body 8, said bush 9 being secured to a contracted portion 10 of the rod or tube 2. Located underneath the outer electrode 12 are e.g. a number of compressed mica rings 8, which are compressed by a ring 7 pushed into the outer electrode, said ring being locked by the lower end 13 of the outer electrode 12 being folded around it. The voltage-supply conductor 5 consists, for example, of two intertwined wires, the end of which has been stuck from the inside through an opening in the ring 7 and in the outer electrode 12, where it is secured by means of a weld 14.

From the description of the embodiment it appears that the insulating difficulties hitherto occuring in sparking elements operating at high temperatures have been solved in a very simple and effective manner.

I claim:

1. A low voltage ignition system for use in a high temperature combustion chamber, comprising a thin conductive rod projecting into said chamber from a wall thereof and having an electrode assembly mounted on the face end thereof, said electrode assembly comprising inner and outer concentric electrode means separated by an insulative body, the inner of said electrode means being secured to the free end of said rod, and separate conductor means connecting the outer of said electrode means to a voltage source.

2. A low voltage ignition system according to claim 1 wherein said inner electrode means comprises a ring mounted within an outwardly facing U-shaped bush secured to the free end of said rod.

3. A low voltage ignition system according to claim 2 wherein said outer electrode means comprises an inwardly facing U-shaped bush mounted outside of and with a portion thereof laterally opposing said ring.

4. A low voltage ignition system according to claim 3 wherein said insulative body comprises plural adjoining layers of insulative material mounted between said U- shaped bushes and under compressive force normal to said ring.

References Cited in the file of this patent FOREIGN PATENTS 

